PHOSPHORESCENT  ZING  SULFIDE 


BY 

AI>BERT  H.  BARNETT 


THESIS 

FOR  THK 

DEGREE  O E B A G H E L O R O F S C I E N C E 

IN 

C H E M IC', A L E N G 1 N F. E R 1 N G 


COl.LEGE  OF  LIBEHAF  ARTS  AND  S(’1!;nCFS 

UNIVERSITY  OF  ILLINOIS 


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- -BA'Sil'RIT-T 

ENTITLED _PIiOS?RPJlSSCFJL^:;i_ZJL:iI^  


IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 
DEGREE  OF  BAAb-iiliir__af__SiLipj'2iie 1e c h ? ni  c .•-i. I i? 'rvc  j r. e e r 1 

— - 

I Instructor  in  Charge 

Approved  

HEAD  OF  DEPARTMENT  OF 


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Digitized  by  the  Internet  Archive 
in  2016 


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TABLE  OF  COFTSFTS. 

PAGE. 

I.  HISTORIC:.! L. 

II. EXPERIl.lEirTAL 

1.  Thermite  Method 4. 

2.  MacBougall,  TTright  and  Stewart 

Method 4. 

3.  Hofmann  and  Dacca  Method 8. 

4.  Modification  Method 9. 

III.CONCIU^'IOIIS 13. 

BIBLIOGRAPHY  15. 


-1- 


ACKNOWIEDGf®NT. 

The  writer  v/ishes  to  express  his  very  sincere 
thnnJcs  to  Dr.  B.S.  Hopkins  for  his  kindly  criticism  and 
helpful  suggestions  rendered  during  the  preparation  of 
this  thesis. 


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PEOSPHORgSC'^lTT  ZIImG  STTIFIDE. 

I.  HT.^TOPTGAI 

Many  substances,  ivhen  eicposed  to  some  source  of 
light  such  as  the  sun,  possess  the  property  of  becoming 
themselves  self  luminescent.  That  is,  they  will  glow  for 
some  time  after  the  exciting  source  has  been  removed. 

This  very  interesting  phenomenon  is  knoivn  as  phosphores- 
cence. If  the  period  in  which  the  bodies  retain  this  light 
is  so  short  that  it  seems  to  disappear  simultaneously  with 
the  exciting  medium,  we  have  fluorescence.  The  difference, 
then,  between  phosphorescence  and  fluorescence  is  merely 
the  length  of  time  in  which  the  light  can  be  retained.  One 
of  the  strange  features  connected  with  this  form  of  light 
emission  is  that  there  is  no  apparent  rise  in  tempera-ture 
accompanying  its  production. 

Por  a great  many  years,  no  distinction  v/as  made  be- 
tween the  glowing  of  phosphorus  caused  by  the  oxidation  of 
its  vapors  and  phosphorescence.  As  a matter  of  fact,  when- 
ever the  latter  was  found  to  exist  it  was  attributed  to  the 

1 

prescence  of  the  former  element,  in  1768,  J.  Canton  heat- 
ed a mixture  of  egg  shells  and  sulfur  and  was  surprised  to 
find  that  the  product  glov^red  after  exposure  to  sunlight. 

His  observations  and  experiments  were  published  under  the 
heading,  ‘ nn  easy  method  of  making  a phosphorus  that  will 
imbibe  and  emit  light”.  His  product  was  later  known  as 


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Canton's  Phosphorus,  He  also  found  that  upon  heating  his 
compound  after  excitation,  a stronger  phosphorescence  was 

2 

produced  but  of  shorter  duration.  A few  years  later  beebeek 
discovered  that  short  wave  lengths  produced  the  most  intense 
illumination  when  used  for  excitation  and  that  red  light 
quenched  the  intensity. 

The  compounds  that  have  been  found  to  phosphoresce 
with  the  greatest  intensity  are  the  sulfides  of  the  alkali 
earths,  HaS,  Gab,  Srb  and  zinc  sulfide.  However,  the  liter- 
ature on  the  subject  is  characterized  by  its  contradictory 
character  and  vagueness.  in  this  work  it  was  endeavored  to 
determine  the  best  method  of  preparing  phosphorescent  zinc 
sulfide  and  also  to  study  the  conditions  that  caused  phos- 
phorescence 

In  1686,  bidot^  prepared  phosphorescent  zinc  sulfide 

by  heating  the  crystalline  sulfide  for  4-5  hours  in  an  atmos- 

4 

phere  of  sulfur  dioxide.  Two  years  later,  Verneuil  discov- 
ered that  he  could  obtain  a phosphorescent  compound  by  heat- 
ing precipitated  zinc  sulfide  to  redness  in  the  preseence  of 

alkali  chlorides  or  the  sulfides  of  other  metals.  In  1699, 

5 

Moure lo  found  some  natural  zinc  sulfide  crystals  v^hich 
phos'-'horesced  after  exposure  to  light.  This  led  to  mi-ch 
discussion  as  to  the  probable  exi stance  of  pure  phosphorescent 
substances  and  just  what  impurities  were  necessary  for  its 
production. 

E3q)erlments  conducted  independently  by  Grune  and 

7 

Hofmann  & fiucca,  in  1904,  on  methods  of  producing  phosphor- 


^ 

escent  zinc  sulfide  seemed  to  indicate  that,- 

1,  The  intensity  of  phosphorescence  diminished  with  an 
increase  in  purity, 

S.  3mall  traces  of  impurities  such  as  magnesium  and  man- 
ganese greatly  increased  the  intensity  of  the  phosphorescence. 

3.  The  addition  of  some  sodium  chloride  had  a beneficial 
effect. 

4.  Certain  metals  such  as  iron,  cobalt  and  chromium 

were  detrimental  to  the  production  of  phosphorescent  compounds. 

in  a paper  published  in  1917  by  Maci)ougall,  v/right  and 
Stewart  some  of  the  above  factors  were  verified  and  the  quant- 
ities of  impurities  necessary  were  determined. 

Phosphorescence  can  be  elicited  by  either  magnesium  ribbon, 
sunlight,  cathode  rays,  x-rays,  mercury  arc  or  an  electric 
globe. 


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The  following  methods  of  preparing  phosphorescent  zinc 
sulfide  were  investigated, - 

1.  Thermite  Method. 

2.  iiacDougall,  Wright  and  Etewart  Method. 

3.  Hof  mann  and  lihicca  Method. 

4.  Modification  Method. 

1.  TES:miTE  MSTiiOH. 

If  a quantity  of  zinc  dust  and  amorphous  sulfur  are 
mixed  in  molecular  proportions,  that  is  65  parts  of  zinc  to 
3E  parts  of  sulfur  by  weight,  and  then  heated,  a very  violent 
reaction  takes  place  and  zinc  sulfide  is  produced.  If  a small 
amount  of  a metallic  impurity  is  added  to  the  mixture  and  the 
operation  repeated  v/e  have  all  the  conditions  necessary  for 
the  production  of  a phosphorescent  compound.  Hov;ever,  this 
method  proved  unsucessful  because  a uniform  product  could  not 
be  obtained.  Eome  of  the  sulfide  glowed  more  intensely  th^in 
the  rest. 

2.  MACHOTJGAIL,  .>KIEHT  aHJJ  ETB.vAHT  l^THOD. 

Zinc  chloride  sticks  were  dissolved  in  water  and  the 
solution  was  made  alkaline,  a considerable  quantity  of  ferric 
hydroxide  precipitated  so  that  the  solution  was  allowed  to 
stand  for  2 days  in  order  to  insure  the  complete  removal  of 
iron  because  of  its  poisonous  effect  on  the  phosphorescence. 


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i‘he  solution  was  then  filtered,  diluted  to  molal,  and  15 
grams  of  sodium  chloride  were  added  per  liter.  15  cc.  of  a 
thousandth  grsjn  molecular  solution  of  copper  chloride  was 
added  to  100  cc.  of  the  zinc  chloride  and  the  zinc  sulfide 
was  then  precipitated  with  hydrogen  sulfide.  ‘i‘he  precipitate 
was  filtered,  dried  at  about  100°  and  ground  in  a porcelain 
mortar. 

The  ease  with  ?/hich  the  samples  are  contaminated 
cannot  be  overemphasized,  .absorption  of  gases  from  the  air, 
dust,  or  contact  with  metallic  objects  have  a very  deleterious 
effect. 

later,  it  was  found  more  practical  to  use  about  500cc. 
of  zinc  chloride  at  a time  instead  of  lOOce.  because  comparative 
results  were  not  obtainable  from  different  batches  of  stock 
solution.  One  reason  for  this  difference  was  the  difficulty 
in  precipitating  exactly  the  same  amount  of  sulfide  each  time. 
The  best  results  were  obtainable  when  about  one-half  of  the 
entire  amount  of  sulfide  was  precipitated.  If  all  of  the  sul- 
fide was  brought  down  the  results  were  much  inferior.  Since 
hydrogen  sulfide  was  used  for  the  precipitation,  it  was  not 
possible  to  bring  down  exactly  one-half  of  the  zinc  each  time. 
Ammonium  sulfide  was  tried  but  it  gave  inferior  results. 

The  degree  of  phosphorescence  was  improved  by  sieving 
the  zinc  sulfide  thru  silk,  because  of  the  danger  and  ease  of 
contamination,  a metal  sieve  was  not  used.  instead,  the  piece 
of  silk  was  placed  between  the  wide  ends  of  two  large  funnels. 


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The  latter  were  then  clanged  together. 

il’or  heating  the  samples,  a four  inch  muffle  furnace 
was  found  to  be  the  most  practical,  it  was  modified  by  plac- 
ing a well  fitting  clay  plate  as  a false  bottom, ^ust  above 
the  gas  jet, in  order  to  keep  the  flames  from  the  crucibles 
as  that  would  cause  uneven  heating,  hy  means  of  this  arrange- 
ment about  six  crucibles  could  be  heated  at  the  same  time  if 
necessary.  The  samples  were  heated  at  various  temperatures 
in  order  to  determine  the  affect  of  time  and  heat  on  phosphores- 
cence. A pyrometer  was  used  for  the  temperature  measurements. 

To  determine  v/hen  the  maxiniara  phosphorescence  was  reach- 
ed, samples  were  taken  out  every  two  minutes  with  a porcelain 
spatula  and  tested  immediately  under  sunlight,  magnesium  ribbon 
or  electric  globe.  A small  bottomless  cylinder  with  an  obser- 
vation aperture  on  the  top  was  found  very  useful  for  daylight 
testing.  By  means  of  this  device  the  latter  could  be  performed 
in  the  vicinity  of  the  furnace  as  it  performed  the  function  of 
a dark  room. 

Porcelain  crucibles  were  found  to  be  the  best  although 
not  entirely  satisfactory.  They  were  fouifi  to  be  attached  by 

the  fumes  evolved  during  the  heating  so  that  they  could  only 

be  used  once.  Metal  orjicibles  contaminated  the  product  very 
easily.  The  crucibles  were  kept  loosely  covered  to  prevent 
eny  contamination  from  the  air  and  to  allow  the  fumes  to  escape 
slowly. 

It  was  found  that  phosphorescent  zinc  sulfide  is  much 


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more  sensitive  to  heat  treatment  than  the  sulfides  of  the  alkali 
earths.  In  the  case  of  the  latter,  excellent  results  were  ob- 
tainable between  a wide  range  of  temperatures  and  time  inter- 
vals. I'hat  is,  a sample  could  be  heated  at  850*^  for  anywhere 
from  15-25  minutes  without  any  appreciable  difference  in  the 
degree  of  phosphorescence.  On  the  other  hand,  if  a sample  of 
zinc  sulfide  were  heated  at  the  s.ame  temperature,  between  a 
range  of  four  minutes, the  phosphorescence  would  pass  from  a 
slight  intensity  through  a maximum  point  and  back  to  a low  in- 
tensity again. 

The  following  three  temperatures  and  their  correspond- 
ing time  intervals  were  found  to  be  the  most  practical, - 


Temperature 

Time 

800° 

15  min. 

850° 

12  min. 

900° 

10  rain. 

A.t  higher  temperatures,  the  samples  could  not  be 
tested  rapidly  enough  as  the  time  interval  decreases  with  an 
increase  in  ten^^erature.  At  lov/er  temperatures,  the  products 
were  found  to  be  inferior. 

The  phosphorescence  of  zinc  sulfide  seems  to  be 
more  intense  than  that  of  the  alkali  earths  but  of  a shorter 
duration. 

CRITICISM  OP  MACDOUGAII  , ’/7RIGHT  AITD  STEWART  METHOD. 

1.  The  amount  of  sulfide  precipitated  could  not  be 
accurately  regiilated.  It  was  found  that  the  sulfides  of  cooper 


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and  manganese  precipitated  "before  the  ainc  sulfide  upon  pass- 
ing hydrogen  sulfide  into  the  solution  so  that  the  quantity  of 
impurity  was  not  proportional  to  the  amount  of  zinc  sulfide 
precipitated,  consequently,  duplication  of  results  could  only 
be  accomplished  with  the  greatest  difficulty. 

2.  fhe  amount  of  sodium  chloride  contained  in  the  samples 
depended  upon  the  amount  of  liquid  adsorbed  by  the  percipita-te 
during  filtration  and  consequently  was  a variable  quantity. 

3.  i'he  zinc  chloride  contained  other  impurities  such  as 
cadmium  and  lead  which  were  not  removed  by  this  method. 

3.  HOFMiVM  AFD  BUCCA  TfflTHOB. 

In  this  process,  the  zinc  sulfide  was  precipitated  from 
zinc  ammonium  sulfate  as  the  latter  can  be  prepared  in  a very 
pure  state  by  recrystallization  in  water 

20  grams  of  zinc  ammonium  sulfate,  5 grams  of  sodium 
chloride  and  .4  gram  of  magnesirm  chloride  were  dissolved  in 
460  cc.  of  distilled  water  which  had  been  slightly  acidified 
with  sulfuric  acid.  lOOcc.  of  ammonium  hydroxide  were  then  add- 
ed, the  solution  was  stirred  thoroughly,  and  allov/ed  to  stand 
for  24  hours.  The  precipitation,  drying  and  heating  were  then 
carried  out  as  described  in  the  above  method. 

GP.TTICISM  OF  HOFMm:  AIID  DFCCA  MFtHOB. 

1.  The  amount  of  sodium  chloride  varied  as  in  the  Mac- 
Dougall  Method. 

2.  Its  use  was  limited  to  magnesium  and  manganese. 


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4.  i.'iODT^’ICATIOlT  lifSl'HOjJ. 

I’his  method  might  be  considered  as  a combination  of  the 
good  points  in  the  above  two  methods  and  those  in  Lenard  and 
Xlatt's  method  for  the  production  of  phosphorescent  sulfides 
of  the  alkali  earths. 

Zinc  sulfate  was  used  as  a raw  material  instead  of  the 
chloride  because  the  chlorine  affects  the  phosphorescence  and 
the  amount  of  it  was  regulated  in  the  last  stages  of  this 
procedure  in  order  to  be  able  to  duplicate  results. 

50  grams  of  zinc  sulfate  were  dissolved  in  about  450  cc. 
of  water,  the  solution  was  heated  and  then  acidified  with  5 cc. 
of  nitric  acid,  androgen  sulfide  was  then  passed  in  and  the 
solution  f il tered, thus  eliminating  any  cadmium  or  lead  that 
might  be  present. 

‘rhe  hydrogen  sulfide  was  prepared  by  passing  electrolytic 
hydrogen  thru  boiling  sulfur.  I’he  electrolyte  was  a lO/o  sodium 
hydroxide  solution  and  the  electrodes  of  nickel  gauze.  The 
sulfur  was  purified  with  carbon  disulfide.  The  product  formed 
was  very  pure  but  the  yield  was  small  because  of  the  ease  with 
which  hydrogen  sulfide  decomposes  at  high  temperatures.  Later, 
this  method  was  discontiniied  because  the  samples  were  not  suf- 
ficiently improved  to  v/arrant  its  substitution  for  the  mu.ch 
more  simple  and  efficient  method  of  using  pyrites  and  sulfuric 
acid  in  a kipp  generator,  in  the  latter  method  a purification 
train  was  employed  which  consisted  of  two  units  containing 
cotton,  one  of  sulfuric  acid  and  one  of  distilled  water. 


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-TO- 


The  filtrate  from  the  hj'drogen  snlfide  treatment 
was  treated  with  lOcc.  of  concentrated  nitric  acid  and  boiled 
for  ten  minutes,  20c c.  of  ammonium  hydroxide  were  then  added 
and  the  solution  filtered,  -mmonium  hydroxide  was  then  added 
in  excess  until  the  precipitate  which  first  formed  redissolved. 
The  solution  was  allowed  to  stand  for  48  hours  and  the  ferric 
hydroxide  then  removed  by  filtration.  Hydrogen  sulfide  was 
then  passed  into  the  warmed  filtrate  to  saturation.  The  filter- 
ed zinc  sulfide  was  washed  very  thoroughly,  this  being  the  only 
method  in  which  that  operation  can  be  performed  , j?‘inally,  it 
was  crushed  and  sieved  thru  silk. 

The  impurities  were  introduced  by  placing  lo  cc.  of 
dry  alcohol  in  a porcelain  mortar.  The  active  metals, such  as 
copper  and  manganese , were  dissolved  in  water  and  the  solution 
diluted  so  that  1 cc.  contained  .001  gram  of  metal.  By  means 
of  a capillary  tube  the  required  pjnount  of  impurities  was  add- 
ed to  the  alcohol.  The  flux,  Bad,  was  then  added  in  the  dry 
form  and  finally  the  zinc  sulfide  was  introduced.  The  constit- 
uents were  thoroughly  mixed  by  grinding  until  the  alcohol  had 
entirely  evaporated  giving  a dry  product. 

The  heating  was  carried  out  by  placing  the  porcelain 
crucible  containing  the  sulfide  in  a larger  clay  crucible  and 
putting  a few  crystals  of  sulfur  between  the  two  in  order  to 
have  a red'cing  atmosphere.  Both  crucibles  were  covered  secure- 
ly thus  preventing  any  oxidation  of  the  sulfide. 


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-11- 


For  a phosphorescent  sample  containing  copper,  the  follow- 
ing proportions  were  found  to  he  the  best,- 

4 grams  zinc  sulfide,  .5  gram  sodium  chloride,  .0004  gram 
copper. 

For  a phosphorescent  sample  containing  mnganese,  the 
following  proportions  were  used,- 

4 grams  zinc  sulfide,  .5  gram  sodium  chloride,  .008  grcm 
manganese. 

Uranium,  molybdenum  and  vanadium  were  also  tried  but  the 
results  were  inferior  to  those  obtained  from  copper  and  man- 
ganese. 


1 


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-Id- 


CCITCIFSIOITS. 

The  Modification  Method  was  found  to  be  best  because  it 
removed  all  of  the  impurities  in  the  raw  material  and  also 
gave  restilts  which  could  be  duplicated  at  any  time.  A large 
q uantity  of  pure  zinc  sulfide  could  be  prepa,red  as  a stock 
supply,  which  facilitated  the  rate  at  which  samples  could  be 
prepared. 

The  necessary  constituents  were  found  to  be  the  pure 
sulfide,  an  active  metal  and  a medium  or  flux  thru  which  the 
tv/o  were  brought  into  intimate  contact. 

Upon  heating  a sample  of  zinc  sulfide,  a considerable 
quantity  of  chlorides  are  driven  off  as  fumes.  If  the  sample 
was  heated  longer  than  the  time  required  for  the  production 
of  phosphorescence,  it  was  found  that  the  zinc  sulfide  was 
almost  entirely  crystalline.  This  indicated  that  all  of  the 
necessary  impurities  had  been  evolved  as  chlorides  because 
the  latter  prevent  the  crystalline  formation  due  to  their  high 
vapor  pressure. 

THSCHY. 

The  mechanism  thru  which  phosphorescence  is  produced 
seems  to  be  a chemical  union  of  the  active  metal  with  the  sul- 
fide causing  a very  complex,  unstable  molecular  formation. 

One  molecule  of  Copper,  for  example,  unites  with  a great  number 
of  zinc  sulfide  molecules.  On  the  application  of  pressure 
as  in  grinding,  the  phosphorescence  diminishes. due  to  a dis- 
turbance of  the  unstable  complexity.  The  excitation  by  means 


. '.I-  > y 


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-14- 


of  light  might  cause  electronic  vibrations  in  the  sulfide 
which  continue  for  some  time  after  the  excitation  censes.  The 
wave  length  of  these  vibrations  must  be  within  the  visible 
spectrum  in  order  to  produce  phosphorescence.  The  frequency 
c.an  be  changed  by  temperature  variations  so  that  a sample  which 
phosphoresces  at  ordinary  temper.atures  will  not  do  so  if  the 
latter  is  increased  or  diminished  sufficiently  to  bring  the 
vibrations  beyond  the  visible  spectrum. 


T.V.  Jiiaik  . <'i lli!L'*.  I .‘M. 


‘Ai- 


' *'Tr^ J 6«1  a .??]«•  :P  p. 

I V ■ ,f  ‘ J%.’'*IT  '.■''■y,  ‘ ;k‘-;^.  j; 

n .■  -/w-t  {O^^’r  K^?  tjrtif,  Vn,r.M  tjjj,  i.s)>-^  ■ 

’ ■'  f ‘ t'  ‘ ■ 

fX^SJ^lr  -M  * i\lt,\>l%  f-a  rfexr,?i 

*’  ,,'-  ? •' "■  '.  ^ '^■.  ; 

* ^ V oji^dtlMciTTl^cx^n 

■ ” "“  ' if',  ' • ■ ■-•  _ ' 


? ■ «•  * I'^i  y ^%pT:':ipi‘^at  /^  j.u 

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--U  Ts;i(i>-i,'^'.  tWXiLXr  vi4 

' '''  ^ 


-15- 


BIBIIOGRIPEY. 

1.  — — Phil.  Trans.  ^ (257-344)  1768 

2.  Gothes  Parhen.  ( 3£3  ) 

3.  Compt.  rend.  103  ( 188  ) 1886 

4.  ibid  106  (1104  ) 1888 

5.  ibid  1^  1899 

6 Berichte  ^ (3076  ) 1904 

7. ibid  37  (3407  ) 1904 


Handbnch  der  Spectroscopie  H.  Kayser. 

Phosphorescent  Zinc  Sulfide  R.  Tomeschek. 

Ann.  Physikj^  ( '189  ) 1921 

Phosphorescent  Zinc  Sulfide  MacBougall,etc. 

Jour.  Chem.  Soc.  Ill  (663)  1917 

Phosphorescenz lenard  and  Zlatt. 

Ann.  Physik  (1899-1915) 


